Work apparatus are known whose operation can be influenced by a movable control element via a Bowden cable and an actuable positioning element. The carburetor of an internal combustion engine, which is used as a drive motor of a brushcutter, is controlled via a Bowden cable as a throttle cable. The throttle flap lever of the carburetor is actuable via the Bowden cable wire by a movable throttle lever which is mounted in a handle of the brushcutter. The pivotal region of the throttle flap lever is limited by an idle stop and full-throttle stop. The pivot region of the throttle lever is then greater than that of the throttle flap lever. For this reason, the adjustment must be so matched that the full throttle position of the throttle flap lever corresponds to the full throttle position of the throttle lever.
If the Bowden cable placement is changed, then the adjustment must be newly adapted. Wear and extreme temperatures can also lead to a lengthening of the Bowden cable and change the matching. Then, the throttle flap of the carburetor can still be in part load, for example, in the idle position of the throttle lever and this could lead to excessive engine speed at idle. The situation can also occur that, for full throttle of the throttle lever, the throttle flap is not completely opened and therefore the engine cannot develop its full power.
In a brushcutter, the throttle lever is integrated into a handle of the steering bar. If the position of the steering bar is changed, then the positioning of the Bowden cable is changed. The adjustment is then to be renewed which is especially difficult outdoors and a smooth work sequence is hindered.
An imprecisely adjusted Bowden cable can lead to considerable start problems. If the start throttle position of the throttle flap is determined by latching of the throttle lever in a start position, an imprecisely adjusted Bowden cable leads to an incorrect throttle flap position. For an opening of the throttle flap which is too narrow, the mixture becomes rich and the engine becomes flooded. For a throttle flap opening which is too wide, the mixture becomes lean and no ignitable mixture results in the combustion chamber.
It is an object of the invention to provide a method for making a precise position adjustment of the Bowden cable available between a throttle lever and throttle flap lever.
The method of the invention is for adjusting the idle position of a throttle pull of a portable handheld work apparatus driven by an internal combustion engine having a carburetor, the carburetor having a throttle lever and a throttle flap lever, the throttle pull including a Bowden cable having a cable casing and a cable wire axially guided and axially movable in the cable casing, and the Bowden cable connecting the throttle lever and the throttle flap lever to each other, the throttle lever being movable between a first idle stop and a first full throttle stop and the throttle flap lever also being movable between a second idle stop and a second full throttle stop; and, the throttle pull further including an adjusting device mounted on an apparatus-fixed support location and having a holding element. The method includes the steps of: moving the throttle flap lever in a direction of full throttle utilizing the throttle lever until one of the levers comes into contact with the full throttle stop corresponding thereto; loosening an existing connection between the holding element of the adjusting device and one of the two ends of the cable casing; axially shifting the one end of the cable casing relative to the holding element so far that the throttle lever and the throttle flap lever come into contact engagement with the first and second full throttle stops, respectively; reestablishing the connection between the holding element and the one end of the cable casing; moving the throttle lever so far in a direction toward the first idle stop so that the throttle flap lever comes into contact engagement with the second idle stop; and, moving the throttle lever through a lost motion distance to the first idle stop.
An adjusting device is arranged in the region of one end of the Bowden cable casing between this end and the support location supporting the end fixedly on the apparatus. The adjusting device includes a holding element secured tightly to the support location. This holding element holds one end of the Bowden cable casing under operating conditions. The connection between the holding element and the Bowden cable casing is releasable to adjust the Bowden cable. The end of the Bowden cable casing cannot be displaced axially in the loosened condition. With the axial displaceability, the effect is utilized that a tension load on the Bowden wire for a Bowden cable placed so as to form an arch leads to a pressure loading between the ends of the Bowden cable casing and the particular support positions fixed to the apparatus.
If the Bowden cable is unadjusted so that the throttle flap lever lies at its full throttle stop before the throttle lever has reached its full throttle stop, a corresponding force acts between the Bowden cable end and the holder element. When loosening the connection between the holder element and the end of the Bowden cable casing, the Bowden cable casing displaces itself automatically in the axial direction until the throttle lever also lies against its full throttle stop. In an advantageous configuration, a pressure spring between the longitudinal stop and the corresponding end of the Bowden cable casing prevents an excessive slippage of the end through the holder element. Thereafter, the connection between the holder element and the Bowden cable casing can again be reestablished. After this procedure, the full throttle position of the throttle flap lever is adjusted to the full throttle position of the throttle lever. In the opposite direction, in the idle position of the throttle flap, the end of the Bowden cable wire, which is hooked into the throttle flap lever, can freely displace axially so that the throttle lever can likewise move back to its idle stop. When opening the throttle, only the lost motion of the Bowden cable wire at the throttle flap lever is to be first overcome.
In a preferred embodiment, the adjusting device comprises a latch element, which is secured on the Bowden cable, a holding element fixed to the support location as well as a spring element. The spring element presses the latch element and the holder element together under a pretension so that the holder element engages in the latch element and holds the latch element with a preadjusted holding force.
For a suitable adjustment of the pretension force of the spring element, the holding force between the latch element and the holder element is sufficient to take up the pressure forces at the end of the Bowden cable casing. These pressure forces result from a usual operating load on the Bowden cable wire. However, if, for example, the throttle flap lever lies against its full throttle stop before the throttle lever has reached its full throttle stop, then an additional manual force can be applied to the throttle lever by the operator. With this additional manual force, the holding force of the adjusting device is overcome whereby the throttle lever can likewise be brought into its full throttle position. At the same time, the latch element shifts relative to the holder element into a new latch position wherein the latch element is axially fixed by the holder element. To increase the holding force in the adjusting device, it can be advantageous to mount a pressure spring in the region of the adjusting device between the longitudinal stop and the corresponding end of the Bowden cable casing. In a preferred embodiment, the adjusting device is provided in the region of the control element because here more structural space is present and therefore also an improved access possibility to the adjusting device.
Preferably, the holding element includes a toothed element having a plurality of teeth, which engage in a corresponding counterset of teeth of the latch element. With this arrangement, and for a high holding force, the teeth can be small and arranged closely one next to the other whereby the adjusting operation can take place in fine steps. For this, the latching element is advantageously configured shorter than the holding element and has a fewer number of teeth than the holding element so that the latch element is completely in engagement with the holding element over a long adjusting path. An approximately symmetrical flank form of the teeth can be advantageous. A flank angle of the teeth of less than 90xc2x0 has been shown to be advantageous. When there is an exchange of the Bowden cable, the latch element is released and is pushed in the direction of idle. After seating the new Bowden cable, the throttle lever is brought into the full throttle position in accordance with the above-described procedure and the latch element of the adjusting device is shifted into the new end position thereby. In this way, a precise positioning of the throttle flap is then ensured for the start position.
In an advantageous embodiment of the invention, the holder element is formed by a tube-shaped guide box in which the latch element is guided. A rack is mounted on the inner wall of the box having teeth which mesh with corresponding counterteeth of the latch element lying thereagainst. On the side of the latch element facing away from the rack, a pretensioned spring element is mounted within the box between the corresponding wall thereof and the latch element. This spring element presses the latch element with its counterteeth into the teeth of the rack. To reduce the structural space, the spring element is configured as a leaf spring and is held form tight to reduce the complexity of assembly. The leaf spring has holding angles at the ends thereof which engage about both ends of the latch element. Because of the holding angles, a form tight connected unit is formed comprising the leaf spring and the latch element so that the leaf spring can be moved together with the latch element during the adjustment operation. In this way, a constant applied force is ensured independently of the latch position of the latch element.
A work tool opening is provided in the toothed wall of the box for unlatching the latch device. With the work tool, for example, a screwdriver, a pressure can be applied which works against the pretensioning force of the spring element and, as a consequence thereof, the latch element no longer meshes with the rack and can be manually adjusted. The unit comprising the latch element and the spring element is advantageously configured so as to be mirror symmetrical whereby a tilting is avoided when pressure is applied with the work tool to unlatch the latch element from the rack.